NEW YORK (CNN/Money) - A sweeping post-holiday rally greeted investors Monday, but some are waiting to see if the markets will sustain their euphoria on Tuesday.

A strong year-end rally Monday pushed the Nasdaq composite above 2,000 for the first time in nearly two years, and the Dow Jones industrial average to its best close in more than 21 months.

Investors can expect Tyson Foods Inc., Smithfield Foods Inc., and Boeing Co. to be among individual stocks on the move Tuesday following news after the market closed Monday.

Moody's Investors Service said late Monday that it may cut its debt ratings for Tyson Foods Inc., National Beef Packing Company LLC and Swift & Co., citing concerns about how the discovery of a cow in the United States with mad cow disease will influence the companies' earnings.

Moody's also said it may still cut the long-term ratings of Cargill Inc. and Smithfield Foods Inc. These companies were already on review prior to the mad cow announcement last week.

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Shares of Tyson Foods (TSN: Research, Estimates) finished 47 cents higher at $13.06 while Smithfield Foods (SFD: Research, Estimates) shares ended 85 cents lower to $21.06. Both trade on the New York Stock Exchange.

The Navy said late Monday it ordered 210 F/A-18E/F Super Hornet attack jets worth $8.5 billion from Boeing, and will give the aerospace and defense company another $979 million to develop and demonstrate a new variant with upgraded weapons.

The Navy had previously ordered 222 Super Hornets under a five-year deal that expires in 2004 and had been expected to buy at least 548 more by 2010, according to Boeing's Web site.

Boeing (BA: Research, Estimates) shares rose 1.3 percent to $42.55 in after-hours trading, according to Instinet, after finishing at $42 on the New York Stock Exchange.

With no quarterly earnings announcements scheduled for this week, investors may be paying particular attention to economic news.

Economists foresee a slight uptick in consumer confidence for December, according to a survey by Briefing.com. Market watchers expect the Conference Board's monthly poll, which will be released one hour after trading begins, to edge marginally higher from 91.7 for November to 91.8 for December.

Midwest manufacturing activity, however, is expected to show a slight pullback for December. The Chicago Purchasing Managers Association will release the results of its monthly manufacturing survey Tuesday morning and economists expect the purchasing manager's index (PMI) to slip to 62 for December from 64.1 in November.

And the National Association of Realtors is due to release its latest figures on existing home sales. According to Briefing.com, economists expect sales fell to 6.33 million units for November from 6.35 million units for October.  

--from staff and wire reports